Embodiments of the invention relate generally to synthetic jets and, more particularly, to multi-function synthetic jets.
Synthetic jet actuators are a widely-used technology that generates a synthetic jet of fluid to influence the flow of that fluid over a surface. A typical synthetic jet actuator comprises a housing defining an internal chamber. An orifice is present in a wall of the housing. The actuator further includes a mechanism in or about the housing for periodically changing the volume within the internal chamber so that a flow is generated and projected in an external environment out from the orifice of the housing. This flow can include fluid vortices. Examples of volume changing mechanisms may include, for example, a piston positioned in the jet housing to move fluid in and out of the orifice during reciprocation of the piston or a flexible diaphragm as a wall of the housing. The flexible diaphragm is typically actuated by a piezoelectric actuator or other appropriate means.
Typically, a system is used to create time-harmonic motion of the volume changing mechanism. As the mechanism decreases the chamber volume, fluid is ejected from the chamber through the orifice. As the fluid passes through the orifice, sharp edges of the orifice separate the flow to create vortex sheets that roll up into vortices. These vortices move away from the edges of the orifice under their own self-induced velocity. As the mechanism increases the chamber volume, ambient fluid is drawn into the chamber from large distances from the orifice. Since the vortices have already moved away from the edges of the orifice, they are not affected by the ambient fluid entering into the chamber. As the vortices travel away from the orifice, they synthesize a jet of fluid, i.e., a “synthetic jet.”
To improve the heat transfer path, micro/meso scale devices such as synthetic jets have been proposed as a possible replacement for or augmentation of natural convection in microelectronics devices. Applications may include impingement of a fluid in and around the electronics and printed circuit boards. However, a synthetic jet typically a number of natural frequencies at which the synthetic jet yields superior cooling performance. These natural frequencies include the structural resonant frequency. The structural resonant frequency is caused at the natural frequency of the structure of the synthetic jet, which consists typically of the synthetic jet plates acting as a mass and the elastomeric wall acting as a spring coupled with the air in the synthetic jet volume.
One major use for synthetic jets is in the cooling of heat-producing bodies, which is a concern in many different technologies. As one example, a synthetic jet may be used for thermal management of tight spaces where electronics may be housed and where space for the electronics is a premium. Typically, wireless communication devices such as cellular phones, pagers, two-way radios, and the like, have much of their heat generated in integrated circuit (i.e., IC) packages that are positioned in such tight spaces. Because of the limited space and limited natural convection therein, the heat generated is typically conducted into printed circuit boards and then transferred to the housing interior walls via conduction, convection, and radiative processes. The heat is then typically conducted through the housing walls and to the surrounding ambient environment. The process is typically limited because of the limited opportunity for convection cooling within the housing and over the printed circuit boards. The low thermal conductivity of the fiberglass epoxy resin-based printed circuit boards can lead to high thermal resistance between the heat source and the ambient environment. And, with the advent of smaller enclosures, higher digital clock speeds, greater numbers of power-emitting devices, higher power-density components, and increased expectations for reliability, thermal management issues present an increasing challenge in microelectronics applications.
Typical electronic devices and integrated circuit packages include numerous components to achieve their desired function, such as cooling devices, microphones, speakers, control circuitry, memory devices, and the like. While the use of a synthetic jet over an alternative cooling device, such as an air-cooling fan, saves space within the IC package, advancements in IC packaging are driven by ever-increasing needs for greater miniaturization of electronics packaging and the components therein.
Accordingly, there is a need for a simplified method and apparatus for providing cooling of integrated circuits while minimizing the overall size and complexity of the electronic device.